YVO₄-Based Birefringence Management for Lyot Filtering Suppression in an All-PM Linear-Cavity Mode-Locked Tm-Doped Fiber Laser

All-polarization-maintaining (PM) linear-cavity mode-locked fiber lasers are known for their simplicity, reliability, compactness, and cost efficiency. However, birefringence-induced Lyot filtering (LF) degrades performance by introducing spectral ripples and temporal distortion. This work presents an effective birefringence-management strategy, conceptually similar to the dispersion management, which aims to suppress LF in an all-PM linear-cavity mode-locked Tm-doped fiber laser, using thin YVO4 crystals to compensate the fiber birefringence. A theoretical analysis is developed to describe the scheme of the LF suppression. Experimental results validate the theoretical predictions, demonstrating that a 2-mm YVO4 crystal effectively eliminates LF at a 49-MHz repetition rate, significantly reducing birefringence-induced spectral ripples and improving the pulse quality. The optimized laser generates 206-fs soliton pulses centered at 2000 nm, achieving a 25% broader spectrum and a 15.6% shorter pulse duration, as compared to the operation without the YVO4 crystal. Moreover, the birefringence management enables precise control over the temporal overlap of co-propagating orthogonally polarized pulses in the PM fiber, with experimental results confirming that the enhanced overlap yields shorter pulses. This approach offers a simple and scalable solution for improving ultrafast laser performance without modifying the cavity architecture. The birefringence control framework offers a new design degree of freedom that may benefit potential applications such as optical coding based on laser parametric modulation.